br>Hello,
Nice to be here.
Recently I read an article about the design of acoustic sound receiver features low power operational amplifier. In the article, It said the amplifier has rail to rail input/output and 0.85mA supply current per amplifier while it uses piezo speaker as its microphone that can be attached to easily due to its size and dimension.
As the following circuit shows,it is comprised of of MCP6L91RT-E/OT 10 MHz, 850 µA operational amplifier that is used to amplify the sound signal. The low-pass filter is used to allow low frequency signal to pass while attenuating high frequency signal or above cut-off frequency of the system to prevent distortions and unnecessary signal. The piezo speaker is used as a microphone or a sound receiver in this circuit. Its size and dimensions is well suited for this application.
The datasheet of MCP6L91RT-E/OT:
http://www.kynix.com/uploadfiles/pdf9675/MCP6L91RT-E2fOT_741415.pdf
I have made one now,but I don’t know why it has some noise when I use it in my guitar? Or there are some wrongs in my guitar?
Has anyone tried it? Could you give me some suggestions?

Thank you,
Best regards~ br> br>

br>PrimateSynthesis

br>While I can't see the entire circuit because of that yellow box. There are two things. It's a very high gain amplifier, with a low input impedance. So you are putting a huge load on the pickup, resulting in a tiny voltage, then trying to make up for it with a massive amount of gain. So I'm not surprised that's it's noisy. Piezo pickups are generally used with very high input impedances (eg. 10M), more than regular guitar pickups (eg. 1M). Which makes them prone to noise, audible differences between cables, etc. even with well-designed amplifiers. A good way to get around the impedance/gain problem is to use a discrete JFET before the op-amp. (Also, I would use bypass caps on the power pins, and a op-amp and a cap for V/2 rather than a passive divider.)

If you google, there are a bunch of schematics out there. As well as PCB's and kits. br> br>